seeing as maplins have discontinued the 3.5w 50ohm rheostat what would happen to my circuit if i used the 100ohm ones instead....the only other ones i can get are rated 5w and 100ohm....which one would be better to use....i will be building the circuit designed by the almighty macroman....used on 120mm sunons.... cheers
The rule for rheostats is max current = sq.rt(Wattage/Resistance) Though its fairly safe to add 25% as (a) the current falls as you turn the resistance up, (b) the unused turns take some heat away from the turns in use at high (low resistance) settings. So a 50R 5W will run fans rated up to 400mA (4.8W), a 100R 5W only to 280mA (3.35W). Bad news is Maplin are discontinuing all their 3.5W loudspeaker controls, not just the 50R.
now we have a problem the sunon fans that i got are rated 12 v (obviously) and draw a current of 0.57A so using my l337 physics skills that will draw 6.84W of power....so how would i ever be able to make a rheobus for those fans...now i did see the article on the "rheobus u cant overload" but the reason i liked the macroman design was cause i could switch the fans on and off seperatly....anyone got any ideas???
check out cpemmas sitehere and if u want a power switch for a fan just put it in the red fan wire hope that sorts it out
and you could use a pot with a switch fitted on any solid-state design, take the +12v supply to the switch first, then out the other side to the electronics.
hmmm....im gonna try and kinda use this article... A Rheo Baybus you can't Overload ::writen by:: ::nox|silicon:: to work out my own rheobus and hopefully u guys will be able to tell me wat i need to change...now according to wat he says i should be able to run those big sunons on it and it shouldnt be a problem as such....is there any other things i should know about this circuit???
You'll need big heatsinks, or the 317T will shutdown (won't hurt it but the fans will stop). All the calculations you need here.
cheers for all the info, will propably involve a 40mm fan in the cooling process of the littel heatsink...no that fan wont be on a rheobus so that wont be the next problem.... just askin if i order the 2k potentiometers would single gang, 2kohm linear potentiometer work???
here we go guys...this is what i came up with using my l33t drawing skills... im not too sure wat r3 should, be to take 12v down to normal 5mm led level...any ideas?? also would this circuit work, which is basically designed to be able to switch the fans between the off, full and variable mode at the flick of a switch..... thanks for all the help, and putting up with loadsa dumb questions....
You'll need a "locking both ways, centre off" switch, and single-pole will do. Maplins have them. The led resistor - use linears calculator
just another couple of thoughts....i was reading this other guys way of making one of these and he used a 10kohm potentiometer and his R1 was 1kohm, and according to his calculations he got voltages to the fan from about 1.25 to 11.5....now if i was to use that in my circuit would that still work or would it cancel out the dimming LED as the fans are turned up and down.... he also used two capacitors in his circuit: A 0.1 ìF (microfarad, sometimes also called MFD) ceramic capacitor. This will go across the incoming power leads and smooth out any ripples before it enters the regulator. You can also use mica, monolithic, or any other kind of unpolarized capacitor. A 1 ìF polarized aluminum or tantalum capacitor. This will go across the output leads, and give you a smooth buffer effect when you adjust the output. You can use larger capacitors if you want a larger buffer, although anything over 10 uF is probably overkill. ...that a good idea???
The formula for 317 voltage output is approx. Vout = 1.25 * (1 + R2/R1) so 1k for R1 and 0-10k for R2 will give you 1.25v to 13.75v. But with 12v in you'll only get about 10.3v out at best, so the top end of the pot travel is wasted. And why go down to 1.25v, that just wastes the bottom end of the pot travel. You've got switches to turn the fan off, don't use a low voltage. The input capacitor helps remove noise if the 12v power leads are several inches long, the output improves stability but is optional for fans. For the few cents/pence they cost I fit them. Read the words here or download the 317 datasheet from National Semiconductor for more info. And a linear pot is fine.
so if i put in the capacitors, i would get a cleaner output...well i just read ur site, which has got loads of info and it looks like ill be putting those capacitors in...they wont stop the LED that dims with the speed of the fan from working will they?? also if i use 1kohm for r1 and r2 at 180ohm would that still work with the LED using a 1k linear potentiometer? cpemma, cheers for all the help....
If you only use 180R the output will only go down to 8.2v. Use a 240R. Leds aren't good at dimming, YMMV but I'd cut the 12v current down to about 5mA to give it a start - use linears calculator and multiply resistor value by 4, then get the nearest. The capacitors won't make any difference.
